In multiple stand tandem rolling mills of the cantilever type as constructed in the prior art all of the spindles are mounted on top of a strong, heavy table with the bearings for the upper spindles mounted on top of the bearings for the lower spindles, as shown in FIG. 1.
If it becomes necessary to remove and replace a lower spindle or either of its bearings, in such a prior art mill it is necessary first to remove the upper spindle and its bearings, because access to the components of the lower spindle in each stand cannot be obtained until the corresponding upper spindle has been removed from its mounted position on top of the lower spindle.
As used herein the following terms have the following meanings:
The "stock" is the metal material being rolled.
The "pass line" is the straight line through the mill along which the stock is travelling as it is being rolled.
A "tandem" rolling mill is a mill in which the stock travels along a pass line through multiple stands in sequence.
A "cantilever" rolling mill is a mill in which the work rolls are mounted on portions of the respective spindles which project in cantilevered relationship beyond the front bearings. In other words, the front bearing is positioned on its spindle between the rear bearing and the location of the work roll on the spindle.
In such prior art multiple stand tandem cantilever rolling mills in which the bearings in the upper spindles are mounted on top of the bearings for the lower spindles which, in turn, are mounted on the table, the interstand forces which are created as a result of the dynamics of rolling exert powerful overturning moments on the respective stands, because the stands loom up in tower-like fashion relatively high above the table top. Consequently, the table must be made very strong and rigid to resist these powerful overturning moments. As shown in FIG. 1, the prior art table was a double-layered table with a pair of vertical webs between the two layers of the table for providing the requisite stiffness. In effect, this prior art table was a large box beam of generally rectangular cross sectional configuration.
In addition to the overturnings moments, the interstand forces generated through the dynamics of rolling exert moments on each stand tending to skew the stand about a vertical axis. Such skewing moments are created because the work rolls are positioned on the spindles in cantilevered relationship with respect to the front and rear bearings. A disadvantage of such prior art table-mounted mills is that the skewing forces on the upper spindles are added to the skewing forces directly induced in the lower spindles, thereby increasing the stresses which must be borne by the lower spindles and their bearing mounts and thereby increasing the spindle deflections which may occur. Since the upper spindles are mounted relatively high above the table top in such prior art mills, relatively long fastening studs or long fastening bolts are inherently involved, and therefore the various stresses can cause significant deflections to occur. In other words, the upper spindles are not closely coupled to the table and so it is difficult for their relatively long fastening members to resist significant deflection under stress.
Further, during rolling, the stock exerts a separating force between the upper and lower work rolls in each stand. In such prior art table-mounted mills the upper spindle bearings transfer these separating stresses through relatively long fastening members to the lower spindle bearing mounts, thereby further increasing the stresses which must be borne by the lower spindles and their bearing mounts.
In summary, the prior art rolling mill as shown in FIG. 1 is commercially successful. However, the present invention provides a number of important technological advantages as described below.